Migrate traitlets documentation from __doc__ to help

[tensor-calculus]

Description Of Changes

pyproject.toml

• Bumped minimum supported traitlets version to 5.8.0 from 5.1.0.

plots/declarative.py

• Removed docstrings that were manually assigned to traitlets.__doc__ and instead defined them using the help parameter.
• Built the documentation locally and compared it with the current online documentation; no rendered changes were observed, as expected.
• Verified behavior in Jupyter, including ?, help(), and <TAB> completion, all of which worked as intended.
• Adjusted the formatting of several function bodies: previously they were written in one or two lines, and adding multi-line strings inline was not readable.

PS: This is my first contribution to MetPy. If there is anything specific you’d like me to adjust in this PR or any other areas you think would be helpful for me to work on, I’d be happy to do so.

Checklist

• Closes Use help parameter for traits rather than setting __doc__ #2844

[CLAassistant]

All committers have signed the CLA.

[tensor-calculus]

There seem to be a number of linting errors related to pre-existing docstrings in this file, which were present prior to this PR and were not modified as part of my changes. Since these docstrings are user-facing and feed directly into the rendered documentation, I’m a bit hesitant to alter them solely to satisfy linting.

I’m not entirely sure how to proceed here; if there’s an established ignore or exception mechanism for this situation, please let me know.